1. Field of the Invention
The present invention relates to an apparatus and method for the purification of agricultural animal waste and, more particularly, to a system for treatment of manure and wastewater and the reuse of wastewater produced and as a byproduct of agricultural facilities.
2. Description of the Background Art
Over the past decades there has been a shift from smaller localized family farms toward larger integrated confinement agricultural operations. Specifically, large agricultural operations referred to as concentrated animal feeding operations (CAFO""s) may utilize confinement barns to house a large number of livestock such as swine, poultry or dairy cows. Using the swine industry as an example, often numerous hog-(CAFO""s) are grouped in close proximity forming xe2x80x9cmega-farmsxe2x80x9d which may house tens of thousands of hogs. Similarly, the dairy industry operates using large factory farms that house thousands of animals in a relatively small land area. While these larger agricultural operations have numerous advantages, attendant with these larger facilities are pollution problems relating to the handling and treatment of manure and wastewater (hereinafter collectively xe2x80x9cwastewaterxe2x80x9d). By way of example, pollution problems associated with liquid animal waste, such as produced by the swine industry, include nitrogen, phosphorus, solids, bacteria and foul odors that result from anaerobic digestion. Environmental concerns more specifically center on odor and water quality issues.
Currently, most agricultural facilities use anaerobic digestion for treatment of animal wastes and wastewater. The primary reasons for using anaerobic digestion is simplicity and cost. Wastewater is simply discharged from the animal storage facility into an open lagoon or plurality of lagoons (ponds used to store and treat thousands to millions of gallons of animal waste) where the waste undergoes natural anaerobic digestion. After retention in the lagoon system, wastewater is usually land applied via spray irrigation. However, over forty (40) noxious gases may be emitted from anaerobic lagoons at hog and/or dairy farms including ammonia, methane and hydrogen sulfide. Additionally, the time required for digestion of the organic wastes is relatively long, from weeks to months. Some current regulations require a residence time of 180 days for animal waste facilities using anaerobic lagoons for digestion. Neighbors find odors emanating from lagoons, confinement houses, and fields onto which wastes are sprayed to be a nuisance. In fact, as a result of odor problems associated with anaerobic lagoons, certain states have legally mandated buffer zones or designated land areas between lagoon sites and populated areas.
Oftentimes, the reduction of organics and nutrients within an anaerobic lagoon is minimal and therefore high quantities of nitrogen, phosphorus, etc. are applied to the land during spray irrigation. These nutrients readily build up high residual concentrations in the soil, leach directly into the groundwater or run-off into surface waters causing algal blooms, oxygen deficiencies and fish kills.
New studies have also shown that lagoons are leaking and there have been pollution problems with the groundwater, rivers, lakes and coastal waters primarily in states where the high concentrations of hog or other farms are located. Another problem attendant with traditional anaerobic settling lagoons is that occasionally the water overflows the lagoons or the earthen containment berms collapse, primarily during periods of heavy rainfall, and the wastewater runs-off into streams, rivers and lakes, causing severe pollution problems. When wastewater escapes from these lagoons, either resulting from overflows or other failures, the high concentration of pollutants has adverse effects on the receiving waters and commonly results in groundwater contamination and massive fish and other aquatic life kills.
The most critical problem in the recent past has been with the microorganism Pfiesteria piscicida. Pfiesteria piscicida is a dinoflagellate related to the species of dinoflagellates that cause xe2x80x9cred tidesxe2x80x9d. This bacterium has the ability to take on up to twenty four (24) different forms during its life cycle and can attack and kill fish within hours. Recent outbreaks of Pfiesteria piscicida could be attributed to the increase in nutrients in the water or to the weakening of the fish due to stress caused by lack of oxygen and/or elevated ammonium levels, among other factors.
By way of example, hog anaerobic lagoon liquid effluent has nutrient characteristics including high levels of biochemical oxygen demand (BOD5), Total Nitrogen (TKN) and Total Phosphorus that cannot be decreased to acceptable levels by anaerobic treatment alone.
Even with bacterial digestion within an anaerobic lagoon, significant amounts of sludge accumulate in an anaerobic lagoon. Anaerobic lagoons may fill to capacity fairly quickly which displaces the designed retention capacity of the lagoon fairly quickly and often serve to provide only partial pretreatment.
Hogs produce two to four times as much waste, per hog, as the average human and, in North Carolina alone, hogs produce about 9.5 million tons of manure a year. Dairy cows produce up to 20 times as much waste, per cow, as the average human. Therefore, a great deal of land is required for spreading the highly concentrated waste since often no discharge is permitted from animal waste facilities. Farmers who specialize in raising large quantities of animals are forced by regulations to use larger and larger areas of land in which to spread the large quantities of wastes generated from higher numbers of animals. This has, and will continue, a trend toward having to sacrifice more land to simply dispose of the waste. The land utilized for land spreading of waste cannot be just any land rather must be carefully selected or altered so as to prevent any rainfall runoff discharging into any surface waters. The land must be planted with species capable of tolerating high nitrogen and high phosphorus containing wastes. The farming industry is running out of places to spread or spray the waste from lagoons.
At least one state has imposed a moratorium on new hog farm facility construction until such time as a solution can be devised to resolve agricultural wastewater treatment issues. Additionally, in North Carolina, owners of existing agricultural waste management systems which were constructed prior to Dec. 31, 1993, must register with the state and have their animal waste management plan certified by a technical specialist.
Continuing efforts are being made to improve agricultural and animal waste treatment methods and apparatus. By way of example, note U.S. Pat. No. 5,472,472 to Northrop and U.S. Pat. No. 5,078,882 to Northrop. U.S. Pat. No. 5,472,472, discloses a process for the transformation of animal waste wherein solids are precipitated in a solids reactor, the treated slurry is passed to a bioreactor zone where soluble phosphorus is precipitated with metallic salts, the slurry is aerobically and anaerobically treated to form an active biomass. The aqueous slurry containing bioconverted phosphorus is passed into a polishing ecoreactor zone wherein at least a portion of the slurry is converted to a beneficial humus material. In operation, the system requires numerous chemical feeds and a series of wetland cells comprising microorganisms, animals and plants. See also U.S. Pat. Nos. 4,348,285 and 4,432,869 to Groeneweg et al.; U.S. Pat. No. 5,627,069 to Powlen; U.S. Pat. No. 5,135,659 to Wartanessian and U.S. Pat. No. 5,200,082 to Olsen et al. (relating to pesticide residues); U.S. Pat. No. 5,470,476 to Taboga and U.S. Pat. No. 5,545,560 to Chang.
Another grouping of background patents are those which disclose methods of treating wastewater rich in nutrients. Note U.S. Pat. No. 5,626,644 to Northrop; U.S. Pat. No. 4,721,569 to Northrop; U.S. Pat. No. 4,183,807 to Yoshizawa et al.
Another grouping of background patents are those which disclose methods of producing humus material or spreadable fertilizer from animal waste. By way of example see U.S. Pat. No. 5,538,529 to Northrop; U.S. Pat. No. 5,525,239 to Duske and U.S. Pat. No. 5,282,879 to Baccarani.
The disclosures of the documents submitted as part of the Information Disclosure Statement previously filed concurrently with U.S. application Ser. No. 09/167,275 are incorporated by reference in their entirety.
Not withstanding the existence of such prior art treatment systems, it remains clear there is a need for a wastewater treatment system that reduces the retention time of waste in an open lagoon, may operate as a xe2x80x9cclosed-loopxe2x80x9d system with no land application of waste or, during treatment, significantly reduces the amount of nutrient load in the treated wastewater such that less land is required for land application and recycles and reuses water for use by agricultural animals.
Efforts to improve the methods and apparatus to reduce the deleterious effects of wastewater byproducts from agriculture continue. Accordingly, it is an object of the invention to provide an improvement that overcomes inadequacies of the prior art method and apparatus and provides an improvement, which is a significant contribution to the advancement of the art.
Another object of this invention is to provide a new and improved system for purification of agricultural animal waste that has all the advantages and none of the disadvantages of the prior art.
A further object of the present invention is to provide a system to treat manure and wastewater having a minimal impact on the environment.
Another object of the invention is to provide an approved treatment apparatus and method that significantly reduces the amount of nutrient loading in the treated wastewater such that less land is required for spray irrigation or land application.
Another object of the invention is to provide an apparatus and method of treating agricultural wastewater whereby minimal or no land application is required.
Another object of the invention is to provide an effective treatment of the wastewater using methods that will greatly reduce, if not eliminate, the foul odors associated with anaerobic lagoons and providing a closed loop treatment process.
Another object of the invention is to treat wastewater without greatly reducing the nutrients present in any recovered sludge.
Another object of the invention is the creation of an efficient, impervious aerobic treatment basin that does not consume a large surface area and that does not pose an impact to groundwater.
Another object of the invention is to provide drinking water suitable for agricultural livestock through use of ozone purification of treated wastewater.
Another object of the invention is to provide a system for the purification of agricultural wastewater that is economically feasible.
Another object of the invention is to provide an apparatus and method more energy efficient than currently available treatment systems.
Another object of the invention is to provide an apparatus and method for treatment of agricultural waste, which meets regulatory compliance.
The foregoing has outlined some of the pertinent objects of the invention. These objects should be construed to merely be illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.
For the purposes of summarizing the invention, the present invention is drawn to a unique apparatus and method for treating and reusing the wastewater discharged from agricultural animal farms. The apparatus and method of the present invention may be readily sized and configured depending upon the amount and constituent(s) of the wastewater to be treated. In a first embodiment, the apparatus and method of the present invention is designed to be a zero discharge system in which no wastewater will be discharged or land applied. In use, the apparatus and method of the first embodiment may actually require addition of make-up water during periods of low rainfall to make-up water losses due to evaporation and drift. It is contemplated that the only byproduct of the apparatus and method of the first embodiment may be a beneficial organic fertilizer if a sufficient number of installations are operated.
In a first embodiment, typical of that which may occur at a hog farm installation, the apparatus and treatment method of the present invention will consist of several phases following delivery of the wastewater effluent from the agricultural sites. The wastewater influent is first passed through a mechanical screen where bulk solids (in the case of hog farm wastewater this will consist primarily of corn) are separated and partially de-watered. The screened influent then undergoes primary aeration in a primary aeration reservoir which may occur in either an earthen basin or above ground storage tank where it undergoes aerobic digestion utilizing specially selected bacteria. As used herein, primary or secondary aeration reservoir shall refer broadly to any container or receptacle for retaining wastewater. Basin shall refer to any in-ground primary or secondary aeration reservoir in which aerobic digestion may occur. Preferably the basin is plastic lined or otherwise resistant to ground water or seepage. A basin may alternatively be termed a cell, lagoon, pond or reservoir. Tank shall refer to any above-ground primary or secondary aeration reservoir in which aerobic digestion may occur. Treatment in the aeration reservoirs, whether basin or tank, serves to break down organics and oxidize both macro- and micro-nutrients resulting in the reduction of BOD5, COD, TKN, and ammonium-nitrogen. After treatment in the primary aeration reservoir, the wastewater may be used to wash the floors of the animal houses or undergo a purification phase including solids separation, nitrification, denitrification, filtration and sterilization.
Periodic flushing of the sub-floor space beneath the pens in the animal houses serves to carry fresh waste to the treatment system. By using aerobically treated wastewater which has undergone aerobic treatment in a primary aeration reservoir, the sub-floor space is thereby incorporated into the treatment system. Aerobically treated wastewater carries with it the beneficial bacteria to begin the digestion of organics beneath the floor of the animal houses without the presence or generation of noxious gases, which can be a problem associated with flushing with anaerobic treated water. This will help to reduce health risks associated with the noxious gases (irritation of animal""s lungs bring about the onset of pneumonia) but also with pathogenic bacteria associated with the anaerobic waste.
In a preferred embodiment, the solids separation phase (clarification process) will occur in above-ground conical bottom tanks and nitrification/denitrification phases may take place in above-ground tanks or an in-ground basin whereby suspended solids removal will occur as well as nitrification followed by subsequent denitrification for nitrate reduction. The clarification process may be facilitated through use of polymer addition. The precipitated solids following polymer addition will be sent first to a decanting thickening tank for sludge thickening and then to a plurality of drying beds for de-watering and subsequent removal. The aerobically digested sludge will remain on the plurality of drying beds for a short period of time, to reduce water content, and since it is an aerobic not anaerobic sludge, odor should be greatly reduced or eliminated.
Clarified wastewater having gone through the solids separation phase then undergoes secondary aeration to further oxidize organics promoting nitrification, ammonia to nitrate. This step is followed by an anoxic denitrification phase, nitrate to nitrogen gas (N2) which makes up 78% of the earth""s atmosphere, whereby the wastewater enters an anoxic environment for removal of nitrates prior to final treatment. The denitrification occurs in an anoxic treatment reservoir which comprises either an in-ground basin or above-ground tank. In a further refinement, the anoxic treatment reservoir may be covered to aid in the reduction of noxious odors.
Specially selected and propagated bacteria are utilized in both the secondary aeration/nitrification and anoxic denitrification treatment steps.
The final phase of treatment consists of reusing the treated wastewater. Effluent from the denitrification phase undergoes filtration and sterilization using ozone to provide drinking and misting water to the animals. Filtration with multiple filter media serves to remove turbidity, suspended solids, taste, odor and residual organics from the water prior to ozonation. Ozone will provide further oxidation of organics and disinfection of the wastewater resulting in drinking water suitable for animal consumption and/or misting water to cool the animals during warm temperatures. The first embodiment of the present invention requires no land application of agricultural animal waste and drastically improves the quality of recycled water.
In a second embodiment, typical of that which may occur at a dairy farm installation or CAFO, the apparatus and treatment method of the present invention will consist of several phases following delivery of the wastewater effluent from the agricultural sites.
The first phase of treatment is a bulk solids separation step in which the solid manure is separated from the liquids. The solid waste will then be dried and composted generating a nutrient rich organic fertilizer.
The second phase of treatment, following solids separation, will include a primary treatment in an aeration reservoir dimensioned to accommodate the size of the agricultural facility and which will accommodate an increase in population for future growth. Primary aerobic treatment in the primary aeration reservoir with bacteria will greatly reduce organics and odor as well as promote nitrification of the nitrogenous waste (converting ammonia to nitrates). Preferably, the primary aeration reservoir incorporates an energy efficient aeration/circulation system to promote mixing and oxygenation. In the aerobic phase of treatment, odor elimination will occur within hours of system start-up and significant organics reduction as well as nitrification will occur on a daily basis. Specialized bacteria will be isolated and propagated specific for the dairy waste which will create a selective dominance within the aeration reservoir and enhance the digestion of the wastes. We refer to this selective dominance as bioaugmentation.
The third phase of the process is a solids precipitation step which is primarily for phosphorus removal (clarification means). It is anticipated that the clarified water will be virtually phosphorus free. The nutrient rich accumulated sludge is dried on-site in drying beds followed by deactivation for use as solid fertilizer.
The fourth phase of treatment is a secondary aeration step utilizing specially selected and propagated bacteria to promote further nitrification in a secondary aeration reservoir dimensioned to retain partially treated wastewater for several days. This step will begin reducing the nitrogen concentration in the waste stream by oxidizing ammonia to nitrates.
The fifth phase of treatment will include an anoxic basin or tank that is sized to handle up to several days retention for anoxic processes including denitrification, converting nitrates to nitrogen gas. The denitrification phase of treatment may take place in existing waste lagoons. In a further refinement, this phase may also utilize bacteria to aid in the conversion to nitrogen gas. This phase will be variable depending on the seasonal nutrient demands imposed by the crops. It can be omitted if high quantities of nutrients including nitrate-nitrogen and phosphate are required by the crops or maximized if little quantities of these nutrients are required.
The apparatus and method of the second embodiment will have means for controlling the nutrient levels that are applied to the crop land via spray irrigating from the various stages of treatment.
The optional final phase of treatment, including filtration and sterilization of effluent using of ozone, allows for of reusing the treated wastewater for activities including livestock bathing and cooling, land application to crops or discharge (with a significantly reduced nutrient content).
The foregoing has outlined rather broadly the more pertinent and important features of the present invention. The detailed description of the invention that follows is offered so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the disclosed specific embodiment may be utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent construction does not depart from the spirit and scope of the invention as set forth in the appended claims.